Thyroliberin (TRH) induced growth hormone (GH) release: test of maturation of hypothalamo-pituitary axis in postnatal rat.
Small doses of TRH elicit GH release from rat pituitary provided the pituitary lacks CNS influences (e.g. in vitro or in ectopic pituitaries). We have found previously that hypothalamic regulation of TSH secretion matures between the 5th and 12th postnatal day. Therefore the possibility of TRH induced GH release was investigated in neonatal rats. GH concentration was measured by RIA at 10 min after s.c. TRH administration (4.1 pmol g-1 BW) into female Wistar rats at the age 3, 9, 12, 15, 21, 30 and 100 days. Control animals were injected the same volume (1 microliter g-1 BW) of saline. Serum GH in saline treated animals gradually decreased during postnatal ontogenesis. The TRH induced increase of serum GH level decreased during maturation: the most marked response was found at 3 days, it was somewhat lessened but still significant at 9 days and was absent in 12, 15, 30 days old and adult animals. Surprisingly, in 21 days old animals the increase of GH after TRH administration was again present. We conclude that the ability of TRH to elicit GH release in newborn rats may depend on the maturity of the hypothalamo-pituitary axis. The effect of hypothalamic somatostatin is likely to inhibit such a response at the pituitary level in older rats.
D000818:Animals; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D007030:Hypothalamo-Hypophyseal System / Q000254:growth & development*; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone
D013973:Thyrotropin-Releasing Hormone; D013006:Growth Hormone